Photic regulation of circadian rhythms and the expression of p75 neurotrophin receptor immunoreactivity in the suprachiasmatic nucleus in rats

Neurotrophic factors have been implicated in the mechanism underlying photi c regulation of circadian rhythms in mammals. In rats, the most abundant ne urotrophin receptor found in the suprachiasmatic nucleus (SCN), the circadi an clock, is the low affinity p75 neurotrophin receptor (p75NTR). This rece ptor is expressed by retinal afferents of the SCN, but nothing is known abo ut its role in photic regulation of circadian rhythms. We show here that ne onatal treatment with the retinal neurotoxin, monosodium glutamate (MSG), w hich has no effect on photic entrainment of circadian rhythms, nearly compl etely abolished p75NTR immunoreactivity in the SCN in rats. These findings suggest that p75NTR from retinal sources do not play an essential role in t he mechanism mediating photic entrainment of circadian rhythms in rats. (C) 2001 Elsevier Science B.V. All rights reserved.